1. Field of the Invention
The present invention relates to a method for manufacturing an infrared detector, and particularly, to a method for manufacturing an infrared detector which is suitable for manufacturing a photovoltaic type infrared detector by realizing p-n junction on an HgCdTe substrate without a damage using a diffusion method using hydrogen plasma.
2. Description of the Background Art
Generally, a device detecting infrared ray can be divided into a photoconductive type infrared detector which detects a change of conductive according to irradiation of infrared ray, and a photovoltaic type infrared detector which detects a change of voltage or current according to application of infrared ray.
The photovoltaic type infrared detector forms a p-n junction of Hg1-xCdxTe, and separates electric charges which are generated by light through an electric field formed on the junction part to detect the infrared ray.
The above Hg1-xCdx Te is a material having the highest detectivity for the infrared ray, and is able to detect the infrared ray of desired wavelength selectively by changing composition (x).
There are conventional methods for manufacturing photovoltaic type infrared detector, that is, a method forming the p-n junction during growing an HdCdTe substrate, a method forming the junction using ionic acceleration by the plasma, and a method using ion implantation.
The method of forming p-n junction with the growth of the HgCdTe substrate forms an n type HgCdTe area in a p type HgCdTe substrate by controlling concentration of carrier during growing the HgCdTe on an upper part of a transparent substrate.
As described above, in order to form junction parts of different conductive types during the growing process of the HgCdTe by controlling the concentration of impurities, the junction is formed on entire surface of a wafer by controlling the concentration of the carrier using a metal organic chemical vapor deposition (MOCVD) method or molecular beam epitaxy (MBE) method.
The above methods form a low concentration n type HgCdTe layer on an upper surface of low concentration p type HgCdTe substrate, and cuts the substrate into unit devices after manufacturing it.
According to the above method, stable p-n junction can be formed without leakage current, however, the processes such as dividing into unit devices are complex and the cost of the vapor deposition method is high, and thereby unit cost of manufacturing is increased.
Also, according to the above method, it is difficult to realize a planar structure, and therefore, it is difficult to realize the infrared detector of two-dimensional focal plane array.
Second method for forming the junction on the HgCdTe substrate is that plasma is formed by mixing methane (CH4) used to etch the HdCdTe and hydrogen gas, and the junction is formed using the plasma. After mixing the methane gas and the hydrogen gas, the ions are accelerated by the plasma, and then, the accelerated ions damage some of the p type HdCdTe substrate. As the HdCdTe substrate is damaged by the accelerated ions, the hydrogen ions are injected into the substrate, and thereby, the n type area is formed on the substrate. However, the above method damages the substrate, and causes the leakage current after manufacturing the device.
The last method is the ion implantation method used in semiconductor processes, for forming the junction on the HgCdTe substrate. The method using the ion implantation process forms the p type HgCdTe substrate, exposes a certain area of the HgCdTe substrate, and changes the conductive type by implanting n type impurity ions into the exposed area.
The ion implantation method as above is able to form the infrared detector array in a plane structure easily, however, heat treatment process which is the post-process after the ion implantation activates the ions, and therefore, the uniform device can not be formed. Also, this method damages the HgCdTe substrate as the ion implantation method, and therefore, the leakage current may be generated.
As described above, according to the conventional methods for forming the infrared detector, the manufacturing cost is high, or the HgCdTe substrate is damaged as the p-n junction is formed. Therefore, the leakage current may be generated when the infrared detector is operated, and the properties are degraded.
Therefore, an object of the present invention is to provide a method for manufacturing an infrared detector which does not damage an HgCdTe substrate of a photovoltaic type infrared detector, and can be manufactured with low manufacturing cost.
To achieve the object of the present invention, as embodied and broadly described herein, there is provided a method for manufacturing an infrared detector comprising the steps of: forming a low concentration p type HgCdTe layer on an upper part of a transparent substrate; forming a diffusion preventing layer with some part exposed on the low concentration p type HgCdTe layer; forming a low concentration n type HgCdTe layer by diffusing hydrogen ions and atoms to the exposed low concentration p type HgCdTe layer using hydrogen plasma, and forming a p-n junction; removing the diffusion preventing layer, and forming an insulating layer on entire upper surfaces of the low concentration p type HgCdTe layer and the low concentration n type HgCdTe layer; forming a contact hole on the insulating layer so as to expose some upper surfaces of the low concentration p type HgCdTe layer and the low concentration n type HgCdTe layer; forming plugs contacted to upper parts of the low concentration p type HgCdTe layer and the low concentration n type HgCdTe layer in the contact holes; and forming a pad contacted to the respective plugs and located on some upper part of the insulating layer to be a predetermined area by depositing and patterning the metal layer on the entire upper surface of the above structure.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.